Regional Impacts
Today
NS: Slight risk of an isolated thundershower over southwestern Nova Scotia this afternoon with locally heavy downpours.
NFLD: Slight risk of some isolated thundershowers today with some locally heavy downpours.
NB/PEI/LAB: None.
Tonight
NB: Risk of an isolated thundershower over northwestern New Brunswick overnight with locally heavy downpours.
NS/PEI/NFLD/LAB: None.
Tomorrow
NB: Risk of an isolated thunderstorm over western New Brunswick in the afternoon with heavy downpours and gusty winds.
NS/PEI/NFLD/LAB: None.
Convective Discussion…
A slightly more active end to the week is in store for Atlantic Canada as a ridge of high pressure over the region begins to erode. A few areas to watch exist today, the first associated with some weak upper troughing with a few embedded vorticity centres extending from Newfoundland down to Cape Cod. This threat area triggered a few elevated thundershowers overnight, but will remain largely offshore as the trough moves east. That being said, a few thundershowers may develop over parts of Newfoundland today and into this evening given sufficient clearing in combination with an approaching 500 mb jet currently centred over Labrador. MUCAPE values over this area should remain fairly low (less than 200 J/kg) but given the relatively high 0 to 6 km shear (35 to 45 knots), there could be just enough energy to get some isolated thundershowers to develop which may produce some locally heavy downpours.
The second area to watch will be over southwestern Nova Scotia this afternoon. The risk here is a bit lower due to a lack of forcing, however higher instability (500 to 750 J/kg MLCAPE) with 20 to 30 knots of effective shear could trigger an isolated thundershower or two if a convergence zone does set up. Anything that does fire here this afternoon will likely be short-lived but with very weak mean wind, they will remain fairly stationary which could lead to some heavy downpours of 10 to 20 mm per hour.
Tonight, a very slow moving surface trough currently over southern Quebec and extending into western Maine will approach northwestern New Brunswick. This could lead to some elevated thundershowers overnight with MUCAPE values of around 500 to 750 J/kg and effective shear of 20 to 30 knots. The timing of initiation will depend on how quickly the 500 mb jet approaches from Southern Ontario but a few strikes are possible before morning.
Tomorrow looks a bit more interesting over western New Brunswick as the aforementioned trough sets up over the area along with a better 500 mb jet setup. Current guidance indicates MLCAPE values could build to around 1000 J/kg which could lead to some marginally severe thunderstorms. There is some uncertainty in the timing of the trough however, with some guidance keeping it over Maine until later in the evening. Nonetheless, the potential does exist for some isolated thunderstorms with heavy downpours and gusty winds, especially along the Maine border.
Thunderstorm Outlook for Today
Thunderstorm Outlook for Tonight
Thunderstorm Outlook for Tomorrow
Forecaster: Copp